Compounds 4',5'-unsaturated nucleosides represented by the formula (I): ##STR2## wherein R represents a hydrogen atom or a hydroxyl group and B represents a base group such as a purine base and pyrimidine base, for example, 4',5'-unsaturated adenosine, are important intermediates for the synthesis of nucleocidine [E. J. Backus, H. D. Tresner and T. H. Campbell, Antibiot. Chemother., Vol. 7 p. 532 (1957)] and augustmycin A. [H. Yuntsen, K. Ohkuma, Y. Ishii and H. Yonehara; J. Antibiot., ser. A. 9 P. 195 (1956)]; nucleocidine and angustmycin A are known to possess potent trypanocidal, antibacterial, and antimicrobial activities.
These compounds and methods of preparation are already known [I. D. Jenkins, J. P. H. Verheyden and J. G. Moffatt, J. Amer. Chem. Soc., Vol. 93 P. 4323 (1971); E. J. Prisbe, J. Smejkal, J. P. H. Verheyden and J. G. Moffatt, J. Org. Chem., Vol. 41 P. 1836 (1976)]. 4',5'-Unsaturated nucleosides have hitherto been synthesized by, for example, the reaction as shown below. ##STR3## Bz: benzoyl Tr: Triphenylmethyl
DBN: 1,5-diazabicyclo[4,3,0]non-5-ene
As is seen in the reaction formula, however, the protection of the base and sugar moieties of nucleoside is required so that the process becomes complicated. Furthermore, undesired side reactions such as halogenation of the base moiety and cyclization take place, resulting in low yield of 4',5'-unsaturated nucleoside. Accordingly, there has been a demand for a solution to these problems.